Physiology 2130 Lecture Notes - Lecture 14: Male Reproductive System, Y Chromosome, Development Of The Gonads
4 Jan 2021
School
Department
Course
Professor
PHYS 2130
July 20
Module 14
Module 14 Lecture: Reproductive System
14.1 Objectives
●Describe the fetal development of the male and female reproductive systems.
●Draw a diagram of the male reproductive system, showing all the structures.
●List the functions of each of the male reproductive organs.
●Define spermatogenesis and describe the sequence of events involved in the entire process.
●Explain the control and regulation of the male reproductive system, including spermatogenesis and
testosterone production.
●List the functions of testosterone.
●Draw a diagram of the female reproductive system, showing all the structures.
●List the functions of each of the female reproductive organs.
●Define oogenesis and describe the sequence of events involved in the entire process.
●List the hormones of the ovaries and explain their function.
●List the events in the menstrual cycle and describe how each hormone is involved in this cycle.
14.2 The Reproductive System → Introduction
●The combined functions of both the male and female reproductive systems are to pass on the genes of
individuals
and to maintain the species
14.3 The Reproductive System → Fetal Development of the Reproductive System
●Each cell in the body contains 23 pairs
of chromosomes → this includes a pair of sex chromosomes
●The sex chromosomes consist of a large X chromosome and a smaller Y chromosome
●All eggs contain an X chromosome while the sperm can carry an X or Y chromosome
●The sex of the future baby is determined at the point of fertilization → if a sperm carrying the X
chromosomes penetrates the egg carrying the X chromosome, then a female will develop (XX)
●If the sperm carrying a Y chromosome fertilized the X chromosome bearing egg, then a male will develop
(XY)
●However, development of each respective reproductive tract does not begin immediately after fertilization
14.4 The Reproductive System → Fetal Development of the
Reproductive System (cont.)
●During the first 6 weeks of development, male and
female embryos contain common (sometimes
indifferent) gonads
●These structures will eventually form the testes in the
male or the ovaries in the female
●There are also two sets of primitive reproductive tracts
→ the mesonephric/ Wolffian Duct
and the
paramesonephric/Mullerian Duct
●With the correct cues, these structures either form the
male or female reproductive tracts
14.5 The Reproductive System → Fetal Development of the Reproductive System (cont.)
●In the developing male embryo, at roughly 6 to 7 weeks the presence of the Y chromosome causes the
indifferent gonads to develop in the testes
●However, in the developing female embryo, at about 9 weeks of development the XX chromosomes are
activated and ovaries develop
●Once the testes or ovaries have developed, the reproductive tracts and external genitalia follow
14.6 The Reproductive System → Fetal Development of the Reproductive System (cont.)
●In the developing male fetus at 7 weeks testicular cells begin
to produce Mullerian inhibiting hormone (MIH)
which
causes the Mullerian duct to regress
●At 9 weeks, testicular cells begin to produce testosterone
●This small surge in testosterone stimulates the Wolffian duct
to develop into the epididymis, vas deferens, seminal vesicles,
and the urethra
●The presence of testosterone also causes the development of
the male external genitalia
●In contrast to the male, the development of the female
reproductive tract and external genitalia requires no hormonal
control
●In the developing female, since there is no Mullerian
inhibiting hormone,
the Mullerian duct develops into the
fallopian tubes, uterus, cervix, and part of the vagine
●Also, since there is no testosterone produced in the female
fetus, the Wolffian duct regresses and the female external
genitalia develop
14.7 The Reproductive System → Introduction (cont.)
●The function of the male reproductive system is to produce the sex steroid testosterone,
to produce sperm
(called spermatogenesis
) and to deliver it to the female vagina
●The female reproductive system is more complex and is responsible for producing the sex steroid estrogen
and the hormone progesterone
●The female reproductive system also produces eggs, receives the sperm,
and provides the optimal
conditions for the development of the fetus
14.8 The Male Reproductive System → Structure
●The external genitalia of the male consists of the penis and scrotum
●The penis is made up of the urethra, glans penis, and the erectile tissue corpus spongiosum and corpus
cavernosum
●The scrotum contains the testes where sperm and testosterone are produced
●After production, the sperm is stored in the epididymis
●During ejaculation, sperm travels through the ductus deferens (vas deferens), mixes with fluid from the
seminal vesicles, passes through the prostate, receives more fluid from the bulbourethral (Cowper’s) gland,
enters the urethra, and passes out through the penis
14.10 The Male Reproductive System → Function
●Seminiferous tubules →
site of spermatogenesis
●Sertoli cells
→ regulate spermatogenesis and maintain the developing sperm cells (called spermatogonia)
○These cells also produce the hormone inhibin,
secrete fluid that pushes the immature sperm to the
epididymis, and form what is called the blood testis barrier
○The blood testis barrier (BTB)
isolates the developing sperm cells from the blood so that immune
cells do not attack these genetically different cells
○If the BTB did not develop properly, immune cells would attack and destroy the developing sperm
resulting in sterility
●Leydig cells →
located in the interstitial space between the seminiferous tubules, produce testosterone
14.11 The Male Reproductive System → Function (cont.)
●The epididymis
is the final maturation area and storage site for sperm
●The vas (or ductus) deferens
carries the sperm from the epididymis to the ejaculatory duct
●The ejaculatory duct drains into the urethra
●Seminal vesicles
contribute a large amount of fluid to the semen during ejaculation
○The fluid, rich in fructose and enzymes, helps to maintain and nourish the sperm
●The prostate gland
also secretes enzymes and fluid that help to neutralize the acid environment of the
urethra and vagina
●The bulbourethral gland (also known as Cowper’s gland)
also secretes a fluid that helps to neutralize the
pH and lubricate the urethra and vagina to create an optimal environment for the sperm
●The urethra
transports sperm during ejaculation and drains the bladder during urination
14.12 The Male Reproductive System → Spermatogenesis
●As the male begins puberty and starts producing testosterone, sperm production (spermatogenesis) begins
●The spermatogonia, or germ cells,
which contain 46 chromosomes and are located at the outer edge of the
seminiferous tubules, divide by mitosis into two cells → one will continue as a spermatogonia and the other
will develop into a primary spermatocyte (each still containing 46 chromosomes)
●The primary spermatocyte divides by meiosis into two secondary spermatocyte (during first meiotic
division) and then into four spermatid (during second meiotic division)
●Throughout this process, the dividing cells, which are surrounded and nourished by the Sertoli cells, work
their way to the center of the tubule
●The spermatids develop into sperm cells, where they are released by the Sertoli cells into the lumen of the
seminiferous tubules
●This whole process takes 64 days to complete and ends with 4 sperm cells that contains 23 chromosomes
each → half of the original number
